Posted
by
Soulskill
on Wednesday March 06, 2013 @06:10PM
from the life-will-find-a-way dept.

tcd004 writes "An article at PBS begins, 'Imagine this crazy scenario: A space vehicle we've sent to a distant planet to search for life touches down in an icy area. The heat from the spacecraft's internal power system warms the ice, and water forms below the landing gear of the craft. And on the landing gear is something found on every surface on planet Earth... bacteria. Lots of them. If those spore-forming bacteria found themselves in a moist environment with a temperature range they could tolerate, they might just make themselves at home and thrive and then, well... the extraterrestrial life that we'd been searching for might just turn out to be Earth life we introduced.' The article goes on to talk about NASA's efforts to prevent situations like this. It's a job for the Office of Planetary Protection. They give some examples, including the procedure for sterilizing the Curiosity Rover: 'Pieces of equipment that could tolerate high heat were subjected to temperatures of 230 to 295 degrees Fahrenheit for up to 144 hours. And surfaces were wiped down with alcohol and tested regularly.'"

Meteors from earth have probably peppered the other planets anyway. Some bacteria spores can survive inside them. So they are probably already contaminated. And in any case we could compare the DNA to see if it is from earth.

IANA physical biologist, but I did look into this question a bit from a systems point of view a few years ago. The key thing would be the minimizing of the energy required to sustain the structure while at the same time allowing maximal adaptability. Or, more abstractly, the 'fitness' of each amino acid pairing for the general task.

There is certainly a large element of chance, but it's probable that the four amino acids that ended up being used are pretty close to the optimal set. This derives from a general evolutionary model, where various things happened by chance, and the ones that worked best for the situation (I could have said 'survived' but that carries too much baggage) would tend to be the ones that were incorporated.

Otherwise, one is arguing that a single chance pairing of amino acids just happened to work, and no others were (in an analogous sense) 'tried' in the right conditions. To my mind, it's more likely that many combinations came together, and one was more successful. It might even be that there was a sequence of such cases - maybe (hypothetical example) when the G and C bases bond together, they float better in a solution with a pH of 7.2 or some such thing.

I prefer to think that certain bases were more available, or just happened to work better under the conditions, and so they got used while others that were 'almost as good' didn't, or didn't for very long. In this case (again with little biological background), things like requiring just enough energy to be split apart, or fitting just right together with the splitting mechanism, or any of several other criteria including environmental ones such as 'in this temperature and pH range') would all be factors. I suspect some very interesting analysis and experiments could be done on this.

Ok, I'm not a complete nutjob here, and I understand two parts of why they bother, first the agency is there to protect our own planet from samples coming back: if the moon or Mars supported life for a few billion years it might become horribly invasive when brought back into the paradise that is our planet, so there is that. Second, they don't want a bacteria covered microscope looking for Martian bacteria because that would kinda nullify the results.

But anyway, I care. I personally feel that we have a responsibility to do whatever we can to take life off this planet ASAP. What if earth is rendered uninhabitable by some unforeseeable cosmic event? As far as we know life is unique to this planet and it would be kinda a bummer to see it all get wiped out when there was a chance to let it restart somewhere else. I'm morally opposed to protecting other planets from ourselves.

The whole article they talk about taking care of the solar system for future research, but fuck future research; if we successfully dropped life onto another planet, that would be way more interesting than our typical: "this rock has more iron than that rock," and I really see no need to save those rocks for our great grandchildren at the expense of creating alien life.

That is one of the things they're testing. They see an initial growth defect upon adding the new amino acid. Basically, every place the altered codon is found the resulting protein acts somewhat weird. Biology is flexible and the cells keep going anyway. After a short while, the cells get over the issue one way or another and there is no remaining growth defect apparent.

[A different experimental group...] If you have an ongoing culture and take isolates at incremental time points, the isolates show interesting behavior when compared. Each isolate will outcompete the isolate just prior when in a common culture, as expected. If you compare each isolate to the second back, most (but not all) will win. If you compare each culture to earlier isolates, it is essentially random which one will win. The expectation was that each isolate would outcompete all prior isolates...

The modified cells will lose to normal ones after the initial change... but once they have had time to get over the shock, it then becomes anyone's guess which way any particular competition experiment will go.

I think the group modifying amino acids is looking to convert them all to types not found in nature... resulting in E. coli with no natural amino acids. At that point, things start to get real interesting. Lots of aspects of our biology are tuned in some way to deal with the existing distribution of amino acids, so these highly modified cells will have lots of changes to lots of systems. Evolution is a really powerful thing. Once you start feeding the culture with less and less of the new amino acids, the cells will figure out how to synthesize them and do so efficiently. Some metabolic circuits will be tweaked, others will be scrapped and scrambled whole-sale.